Attack Rate-Patient Number Plot for Analysis of Food Poisoning Caused by Microbes and Plant or Animal Toxins

Abstract

The number of food consumers (eaters) and patients per outbreak followed a log-normal distribution in food poisoning caused by microbes. In contrast, it followed a scale-free distribution in food poisoning caused by plant or animal toxins. Attack rates of the individual outbreaks were distributed continuously and almost linearly from ＞ 0 to 1 for all the food poisoning cases, i.e., they could not be represented by median and standard deviation. For simultaneous monitoring of the number of patients and the attack rate in individual outbreaks, the number of patients was plotted on the x-axis in the logarithmic scale against the attack rate on the y-axis in the normal scale. This led to the formation of plots characterized by repeating arcs, assuming the shape of a butterfly with extended wings when viewed from above, which was called “backbone configuration.” The butterfly-shaped plot patterns were generally stable over time, although it varied depending on the pathogens, implicated facilities and their combinations. The backbone configuration was reproduced assuming that the number of patients per outbreak was distributed continuously from 1 to the number of eaters per outbreak.